Questions like this are a really tough call to answer. My guess is that the fish may have been infested with internal parasites, a lot of wild-caught fishes are. Sometimes, if dead imports are left in a tank for a time you often will see parasitic crustaceans (isopods,etc) & other nasties crawl out of the carcass. How is the other BG acting
Also, black ghosts tend to be interspecifically aggressive so perhaps the larger ghost had a hand in his demise although you state that there was no apparent external damage. Perhaps he 'electrocuted' his rival! Only half kidding here, ghosts emit electrical charges mainly for orientation & food location in dark or murky conditions. Perhaps they have worked out a method to protect their turf from invaders.
Last edited by viejo; 02-08-2009 at 01:27 PM..